Thermochromic Level Indicator

ABSTRACT

A thermochromic ink or print varnish is formulated and printed to form a level indicator.

RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisional Application Ser. No. 61/663,089, filed Jun. 22, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND Thermochromic Inks

Thermochromic and photochromic encapsulated dyes undergo a color change over a specific temperature range. By way of example, a dye may change from a particular color at low temperature to colorless at a high temperature, such as red at 85° F. and colorless at above 90° F. The color change temperature is controllable, such that the color-change can take place at different temperatures. In one example, the color change may occur at a temperature just below a person's external body temperature so that a color change occurs in response to a human touch.

This variability in the dyes results from selected materials and manufacturing processes. One technique used to produce the thermochromic encapsulated dye is to combine water, dye, and oil, with melamine formaldehyde resin and agitate to create a very fine emulsification. Interfacial tensions are such that the oil and dye end up on the inside of a melamine formaldehyde capsule distributed in primarily the water phase. The melamine formaldehyde substance, while very hard and resistant to breakdown at high temperature, is permeable. A variety of thermochromic inks may be purchased on commercial order, for example, from Chromatic Technologies, Inc. of Colorado Springs, Colo.

U.S. Pat. Nos. 4,421,560 and 4,425,161 entitled “Thermochromic Materials” both state that thermochromic inks can be made with “conventional additives used to improve conventional printing inks.” Nonetheless, there are concerns over what additives may be added to these inks.

U.S. Pat. No. 6,139,779 teaches that it is desirable to minimize the use of certain solvents and other compounds that degrade or destroy the color performance of the dye. In particular, aldehydes, ketones, and diols should be removed from the formulation and replaced with solvents that do not adversely affect the thermochromic pigment. In this regard, solvents having a large molecular weight (i.e. greater than 100) generally are compatible with the thermochromic pigments. The acid content of the formulation may also be adjusted to a value of less than 20 or adjusted to be neutral in the range from 6.5-7.5 pH. These adjustments allow the thermochromic dyes to be added to the formulation without a loss of its color change properties.

Thermochromic dye is often sold in a slurry of encapsulated dye in a water base. It happens that the pH of this slurry is most often neutral in a range from 6.5 to 7.5. When thermochromic dye is added to a formulation that has a pH outside this range, the color change properties are often always lost. This is an irreversible effect and therefore, it is important to adjust the pH prior to adding the thermochromic dye.

Several types of ingredients are traditionally added to ink formulations. The combination of all the ingredients in an ink, other than the pigment, is called the vehicle. The vehicle carries the pigment to the substrate and binds the pigment to the substrate. The correct combination of vehicle ingredients will result in the wetting of an ink. This wetting means that the vehicle forms an absorbed film around the pigment particles. The main ingredient in an ink is the binder. This may be a resin, lacquer or varnish or some other polymer. The binder characteristics vary depending on the type of printing that is being done and the desired final product. The second main ingredient is the colorant itself, for example, as described above. The remaining ingredients are added to enhance the color and printing characteristics of the binder and the colorant. These remaining ingredients may include reducers (solvents), waxes, surfactant, thickeners, driers, and/or UV inhibitors.

Scented Inks

As taught by U.S. Pat. No. 6,454,842, scented inks may be produced using microcapsules to prolong the life of the scent. These scented inks do not use thermochromic materials and may be microencapsulated using an microemulsion that contains a water soluble polymer selected from the group consisting of acrylic, styrenated maleic anhydride, sulfonated polyester, polyamide, and polyurethane or monomers thereof; (ii) a colorant; (iii) water and (iv) scented oil.

Perfumes and other scented materials generally contain ketones and aldehydes that contribute significantly to the scent. Diols, such as glycerol, may be used as solvents. This presents a materials incompatibility issue where these materials are known to degrade the performance of thermochromic dyes. It does not appear that perfumes are used as an ingredient in thermochromic inks.

Metal Deco Applications

Lithography depends upon the separation of oil and water. The oil is the ink and the water is the fountain solution. The fountain solution is acidic to minimize the emulsification of ink. The higher the pH the more scumming occurs; i.e. the movement of ink into areas of the image that are supposed to by free of ink. The acid and other components in fountain solutions destroy the color change characteristics of the thermochromic pigments.

The use of thermochromic inks for metal decoration is an area of special concern. Most metal beverage cans made in the United States are manufactured from aluminum. In Europe and Asia, approximately 55 percent of cans are made of steel and 45 percent are aluminum alloy. Aluminum cans may contain an internal coating to protect the aluminum from beverage corrosion. Chemical compounds used in the internal coating of the can include types of epoxy resin.

Beverage cans are usually filled before the top is crimped in place. The filling and sealing operations are fast and precise. The filling head centers over the can and discharges the beverage to flow down the sides of the can. The lid is placed on the can then crimped in two operations. A seaming head engages the lid from above while a seaming roller to the side curls the edge of the lid around the edge of the can body. The head and roller spin the can in a complete circle to seal all the way around. A pressure roller next drives the two edges together under pressure to make a gas-tight seal. Filled cans usually have pressurized gas inside, which stiffens the filled cans for subsequent handling.

Aluminum cans may be produced through a mechanical cold forming process starting with punching a flat blank from very stiff cold-rolled sheet. This sheet is often made of a material called alloy 3104-H19 or 3004-H19. This material is aluminum with about 1% manganese and 1% magnesium for strength and formability. A flat blank is first formed into a cup about three inches in diameter. This cup is then pushed through a forming process called “ironing” which forms the can. The bottom of the can is also shaped at this time. The malleable metal deforms into the shape of an open-top can.

Plain lids are stamped from a coil of aluminum, typically alloy 5182-H48, and transferred to another press that converts the stamped materials into easy-open ends. The conversion press forms an integral rivet button in the lid and scores the opening, while concurrently forming the tabs in another die from a separate strip of aluminum. The tab is pushed over the button, which is then flattened to form the rivet that attaches the tab to the lid. The top rim of the can is trimmed and pressed inward or “necked” to form a taper conical where the can will later be filled and the lid (usually made of an aluminum alloy with magnesium) attached. The lid components, especially the tabs, may be coated before they are subjected to such manufacturing processes as riveting.

Exterior surfaces of the cans may be coated with inks as shown, by way of example, in U.S. Pat. No. 6,494,950. Polyester resins are often favored for use on the sides of the cans. Epoxy resins are favored for use on the lids, especially where there is a need for improved durability of the coatings. Thermochromic inks may be used as indicators to assess when beverages have reached a particular temperature, such as when a soft drink or a beer is at a temperature that is particularly pleasing to the palate. A variety of polyester-based thermochromic inks are commercially available for coating the sides of the cans. Practically speaking, epoxy-based thermochromic inks are not widely available.

SUMMARY

The present disclosure overcomes the problems outlined above and advances the art by providing thermochromic coatings formed as level indicators.

In one embodiment, a housing is provided with a thermochromic level indicator. The housing mat be, for example, a beverage can or bottle. The housing may also be a gas can, an oil container, a drum of chemicals, a fire extinguisher or other container for functional fluids. The housing has a wall presenting an interior space capable of retaining matter at a first level within the wall. The housing also has an opening or lid that may be opened to permit the matter to exit from within the wall or enter into the wall such that the matter assumes a second level. The wall supports a level indicator, which is formed of thermochromic ink. The thermochromic ink has a color transition temperature capable of acting as a level indicator by sensing temperature of the matter retained within the wall in an intended environment of use as the matter transitions between the first level and the second level. By way of example, the matter may be a beverage and the wall forms at least part of a beverage container.

In one aspect, the level indicator may be printed as an indicia representing an image of an object. The image may be, for example, that of a glass, a thermometer, a rainbow, or a vertically oriented line. Moreover, the level indicator may be printed directly onto the housing or a label that adheres to the housing.

In one embodiment, the housing described above may be used in a method of sensing the level of matter within the housing. This is done by filling the housing with the matter to the first level, chilling the housing to a temperature exceeding a color transition temperature of the thermochromic ink, and removing matter from the housing to arrive at the second level in an environment such that the environmental temperature warms a portion of the thermochromic ink above the second level to a level above the color transition temperature. The color change may then be observed to assess an approximate level of the matter within the housing.

DEFINITIONS

Thermochromic system—A mixture of dyes, developers, solvents, and additives (encapsulated or non-encapsulated) that can undergo reversible color change in response to temperature changes.

Thermochromic ink—A mixture of dyes, developers, solvents, and additives (encapsulated or non-encapsulated) that can undergo reversible color change in response to temperature changes. A thermochromic ink is an example of a thermochromic system.

Photochromic ink—A mixture of dyes, developers, solvents, and additives (encapsulated or non-encapsulated) that can undergo reversible color change in response to exposure to light of various wavelengths.

Full color point—The temperature at which a thermochromic system has achieved maximum color density upon cooling and appears to gain no further color density if cooled to a lower temperature.

Activation temperature—The temperature above which a thermochromic system has almost achieved its final clear or light color end point. The color starts to fade at approximately 4° C. below the activation temperature and will be in between colors within the activation temperature range.

Clearing point—The temperature at which the color of a thermochromic system is diminished to a minimal amount and appears to lose no further color density upon further heating.

Hysteresis—The difference in the temperature profile of a thermo chromic system when heated from the system when cooled.

Hysteresis window—The temperature difference in terms of degrees that a thermochromic system is shifted as measured between the derivative plot of chroma of a spectrophotometer reading between the cooling curve and the heating curve.

Leuco dye—A leuco dye is a dye whose molecules can acquire two forms, one of which is colorless.

Thermochromic Coatings

Thermochromic inks useful on beverage containers and the like contain microcapsules, which encapsulate a thermochromic system mixed with a solvent. The thermochromic system has a material property of a thermally conditional hysteresis window that presents a thermal separation. These inks may be improved according to the instrumentalities described herein by using a co-solvent that is combined with the thermochromic system and selected from the group consisting of derivatives of mysristic acid, derivatives of behenyl acid, derivatives of palmytic acid and combinations thereof. This material may be provided in an effective amount to reduce the thermal separation in the overall ink to a level less than eighty percent of separation that would otherwise occur if the material were not added. This effective amount may range, for example from the 12% to 15% by weight of the composition.

The thermochromic system may contain, for example, at least one chromatic organic compound and co-solvents.

Within the encapsulated thermochromic systems, complexes form between the dye and the weak acid developer that allow the lactone ring structure of the leuco dye to be opened. The nature of the complex is such that the hydroxyl groups of the phenolic developer interact with the open lactone ring structure forming a supra-molecular structure that orders the dyes and developers such that a color is formed. Color forms from this supra-molecular structure because the dye molecule in the ring open structure is cationic in nature and the molecule has extended conjugation allowing absorption in the visible spectrum thus producing a colored species. The color that is perceived by the eye is what visible light is not absorbed by the complex. The nature of the dye/developer complex depends on the molar ratio of dye and developer. The stability of the colored complex is determined by the affinity of the solvent for itself, the developer or the dye/developer complex. In a solid state, below the full color point, the dye/developer complex is stable. In the molten state, the solvent destabilizes the dye/developer complex and the equilibrium is more favorably shifted towards a developer/solvent complex. This happens at temperatures above the full color point because the dye/developer complex is disrupted and the extended conjugation of the Ï

cloud electrons that allow for the absorption of visible light are destroyed.

The melting and crystallization profile of the solvent system determines the nature of the thermochromic system. The full color point of the system occurs when the maximum amount of dye is developed. In a crystallized solvent state, the dye/developer complex is favored where the dye and developer exist in a unique crystallized structure, often intercalating with one another to create an extended conjugated Ï

system. In the molten state, the solvent(s), in excess, have enough kinetic energy to disrupt the stability of the dye/developer complex, and the thermochromic system becomes decolorized.

The addition of a co-solvent with a significantly higher melting point than the other dramatically changes the melting properties of both the solvents. By mixing two solvents that have certain properties, a blend can be achieved that possesses a eutectic melting point. The melting point of a eutectic blend is lower than the melting point of either of the co-solvents alone and the melting point is sharper, occurring over a smaller range of temperatures. The degree of the destabilization of the dye/developer complex can be determined by the choice of solvents. By creating unique eutectic blends, both the clearing point and the full color point can be altered simultaneously. The degree of hysteresis is then shifted in both directions simultaneously as the sharpness of the melting point is increased.

Coating formulations with thermochromic pigments having specific color change performance as a function of temperature may be purchased on commercial order from such companies as Chromatic Technologies of Colorado Springs, Colo. Temperature changes in thermochromic systems are associated with color changes. If this change is plotted on a graph having axes of temperature and color, the curves do not align and are offset between the heating cycle and the cooling cycle. The entire color versus temperature curve has the form of a loop. See generally FIG. 1A where the extent of color change presents a gap 100 a that differs between color change that occurs upon heating 102 versus cooing 103. FIG. 1B presents a relatively larger gap 100 b. Such a result shows that the color of a thermochromic system does not depend only on temperature, but also on the thermal history, i.e. whether the particular color was reached during heating or during cooling. This phenomenon is generally referred to as a hysteresis cycle and specifically referred to herein as color hysteresis or the hysteresis window. Decreasing the width of this hysteresis window to approximately zero would allow for a single value for the full color point and a single value for the clearing point. This would allow for a reliable color transition to be observed regardless of whether the system is being heated or cooled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a thermal hysteresis curve for a thermochromic pigment.

FIG. 1B shows a hysteresis curve for a comparable pigment.

FIG. 2 compares beverage cans that are coated with a thermochromic coating according to the present disclosure and chilled to different temperatures.

FIG. 3 shows a beverage can that is printed with a thermochromic ink to provide an indicator showing an approximate liquid level inside the beverage can.

DETAILED DESCRIPTION

Thermochromic level indicators for use on beverage containers utilize take the principle that beverages which are chilled for serving thereafter warm to ambient temperature. The thermodynamic principles of heat transfer are such that the container wall at a level below the liquid level as the beverage is cooler that the container wall above the liquid level.

In one aspect, beverage manufacturers frequently specify a preferred serving temperature for their products. For example, it is commonly believed that a lager-type of beer should be chilled to about 40° F. (4° C.) or less. Ales (including also pale ales), ambers, and browns have relatively complex flavors that are more easily ascertained if the beverage is served at a slightly warmer temperature, especially 45° F.-55° F. (7° C. to 13° C.). Concerning soft drinks, PepsiCo publishes information indicating that their products are preferably served at an ideal temperature of 42° F. (7° C.±1.8° C.), while Coca Cola® is preferably served at 39° F. (4° C.).

Thermochromic Deactivating Agents

As compared to thermochromic microcapsules, scented microcapsules themselves are relatively insensitive to thermochromic deactivating materials including short chain aldehydes, ketones, and diols. Nonetheless, these materials may permeate to exit the microcapsules and enter into thermochromic microcapsules where they may impair the performance of the thermochromic system in embodiments that combine thermochromic microcapsules with scented microcapsules. While it is permissible that the scented thermochromic ink may contain some of thermochromic deactivating materials in the core material of scented microcapsules, these materials in combination should not make up more than about 30% total weight of the scented thermochromic ink.

Solvents

Solvents for diluting the scenting agent in the core material may suitably include those having low reactivity, large molecular weight (i.e. over 100), and which are relatively non-polar. One solvent that fits this category is cyclohexane, which has low toxicity and works well.

Adjusting the Acid Content

In addition to pH, the acid value may also be considered. The acid value is defined as the number of milligrams of a 0.1 N KOH solution required to neutralize the alkali reactive groups in 1 gram of material under the conditions of ASTM Test Method D-1639-70. High acid number substances have inactivated the thermochromic pigments. Generally, the lower the acid number the better. Ink formulations with an acid value below 20 and not including the harmful solvents described above generally work well without deactivating the thermochromic system. Some higher acid value formulations may be possible but generally it is best to use vehicle ingredients with low acid numbers or to adjust the acid value by adding a an alkali substance. The greatest benefit of a neutral or low acid value vehicle is increased shelf life.

Buffers may be used to minimize the effects of the fountain solution on pigment particles. This is one possible solution to the potential acidity problem of the varnishes. One ingredient often used as a buffer is cream of tartar. A dispersion of cream of tartar and linseed oil can be incorporated into the ink. The net effect is that the pigments in the ink are protected from the acidic fountain solution.

Scented microcapsules, i.e., those having a scenting agent with essentially no thermochromic system components, are less sensitive to acid content than are microcapsules that contain a thermochromic system. Whenever the scented microcapsules will be mixed with thermochromic microcapsules, the component that contains the scented microcapsules preferably should not cause the mixture pH to fall outside the range of 6.5 to 7.5. The pH adjustment may be performed as needed using a proton donor or acceptor, depending on whether the pH must be adjusted up or down. For example, HCl is used to lower the pH. KOH may be used to lower the pH. While pH tolerance sometimes exists in an expanded range between 6.0 and 8.0. A pH below 6.0 and above 8.0 almost always immediately destroys the thermochromic system in an irreversible manner.

Mixing

The thermochromic inks are sold in two ways: 1) as a dry powder and 2) in a water based slurry. Conventional mixing systems exists for both slurry and powder that will allow for consistent and well dispersed pigment, and these may be purchased on commercial order.

Drying Technique

The aqueous slurry can be used to make solvent-based ink formulations by first drying the slurry. In traditional ink manufacturing, there is a technique known as flushing. Many traditional pigments come in slurry form, similar to that of the thermochromic capsules. “Flushing” in traditional manufacturing, means to press most of the water out of the slurry to form what is called a press cake which is then “flushed” into a mixing varnish. The press cake is about 25-40% solids. Because of the hydrophobic properties of the pigment and the varnish, the pigment is mixed into the varnish and away from the water. The water separates from the varnish and is left behind. Flushing with the thermochromic capsules does not work. All of the water stays in the varnish rather than separating.

This mixing technique achieves good dispersion and much improved color intensity over using completely dried thermochromic capsules. Not only is it difficult to get the dried capsules to disperse appropriately, but the drying process may destroy between 10% and 30% of the colorant.

Ultrasound Technique

Microcapsules that have been dried all the way to the consistency of powder are difficult to disperse. The microcapsules tend to aggregate. Too much physical agitation by stirring may damage or denature the dye. The problem may be addressed by adding a solvent to the powder to achieve at least about 50% solids content. Once the solvent and the powder are combined, the container with the mixture is submerged in an ultrasound bath. The vibration breaks up the aggregates and conditions the capsules for addition of the remainder of the vehicle ingredients.

General Procedures for Mixing Formulations

For the applications discussed herein, the technique is essentially that of adding pigment to different media to attain a desired result; that of mimicking the visual appearance of normal pigments while trying to add the dimension of thermal activity to its properties.

In order to add normal pigment to ink, dye, or lacquer, the pigment itself is ground into the base. This disperses the pigment throughout the base. The eye cannot see particles that size, so the pigment will give the base a solid color. The addition of more pigment simply intensifies the color. Since the pigment has a very intense color only about 10% of the final ink is made up of normal pigments. Also, the normal pigment itself is relatively impervious to the effects of solvent and pH.

Others have used thermochromic dyes, however, these attempts have focused simply on the addition of thermochromic capsules to an ink base at random and observing whether or not the capsules maintain their original color-changing properties.

In general, the present disclosure teaches the following procedure for making formulations with thermochromic dyes. If in slurry form, and is intended for addition to a water base ink, the water is removed to give slurry between 80% and 95% solids. This is then mixed with an appropriate ink vehicle.

A base for an ink is developed using off the shelf ingredients. The ink will incorporate, where possible, and compatible with the ink types, solvents with molecular weights larger than 100 and avoid all aldehydes, diols, and ketones, and aromatic compounds. Selection of the ingredients is critical. The important considerations with respect to the ingredients within the ink vehicle deal with the reactivity of these ingredients with the thermochromic capsule and its contents.

Ketones, diols, and aldehyde content is minimized, as well as most mineral spirits, excluding cyclohexane and other chemically similar compounds. Ammonia, and other highly reactive compounds are also avoided. The lower the amounts of these compounds, the better the performance of the thermochromic and the longer the shelf life of the product.

Cyclohexane is effective for the purposes of dispersion of the dry thermochromic powder, or for the cleaning of the press in preparation for printing the thermochromic ink. There are however several other possible options for cleaning or as reducers within the ink itself that will also be effective.

The pH or acid value of the ink base is adjusted before the pigment is added. This can be done by ensuring that each individual component of the base is at the correct pH or acid value or by simply adding a proton donor or proton acceptor to the base itself prior to adding the pigment. The appropriate specific pH is generally neutral, or 7.0. The pH will vary between 6.0 and 8.0 depending on the ink type and the color and batch of the pigment.

Once the slurry and the base have been properly prepared, they are combined. The method of stirring should be low speed with non-metal stir blades. Other additives may be incorporated to keep the pigment suspended. The ink should be stored at room temperature.

Most thermochromic systems undergo a color change from a specific color to colorless (i.e. clear). Therefore, layers of background colors can be provided under thermochromic layers that will only be seen when the thermochromic layer changes to colorless. If an undercoat of yellow is applied to the substrate and then a layer containing blue thermochromic dye is applied the color will appear to change from green to yellow, when what is really happening is that the blue is changing to colorless. Just about any color may be achieved by these mixtures.

The Substrate

All substrates that are made-ready to receive the ink should be approximately neutral in pH, and should not impart any chemicals to the capsule that will have a deleterious effect on it. Many types of paper have relatively low pH that could impact the thermochromic capsules. Low pH could cause serious deterioration in a matter of weeks. If quality control is to be maintained, this aspect of the chemistry should be taken into consideration. Use neutral paper whenever possible. Other substrates may include metal, such as aluminum or steel, glass, plastic, fabric, wood, and other substrates.

Specific Formulations

Specific formulations of thermochromic dye formulations are provided below using the principles and techniques taught above. These embodiments teach by way of specific example, and not by limitation.

Production of scented microcapsules may be performed as reported in U.S. Pat. No. 7,901,772, which is incorporated by reference to the same extent as though fully replicated herein.

Ink embodiments for may contain, in combination, a conventional vehicle, scented microcapsules, and thermochromic microcapsules. The thermochromic microcapsules are preferably present in an amount ranging from 1% to 30% of the coating by weight on a sliding scale. This means that there may be from 1% to 30% if the thermochromic microcapsules and from 30% to 1% of the scented microcapsules. The vehicle contains a solvent is preferably present in an amount ranging from 25% to 75% by weight of the coating, and is most preferably about 50% by weight. The solvent is most preferably xylene.

Example 1 Production of Melamine Resin Membrane/Fragrance Microcapsules (In Situ Polymerization Method)

Step A. Preparation of encapsulation core material (mixture): A mixture comprising 75% of a mint fragrance (X-7028, manufactured by Takasago International Corporation, this also applies to all subsequent references to mint) and 25% of palmitic acid (melting point: 63° C.) is stirred at 70° C., thereby dissolving the palmitic acid in the fragrance. The melting point range (T1-T2) for the resulting mixture is from 5 to 45° C. (confirmed visually). The mixture is held at 55° C. to prevent it solidifying prior to emulsification.

Step B. Preparation of emulsion accelerator liquid: 15% of ethylene maleic anhydride resin (Scripset-520, manufactured by Monsanto Company) and 85% of water are mixed together at 60° C., and the mixture is adjusted to pH 4 using acetic acid.

Step C. Preparation of aqueous solution of melamine resin prepolymer: 15% of a melamine-formaldehyde resin (Sumirez Resin 615K, manufactured by Sumitomo Chemical Co., Ltd.) is dissolved in 85% of water at 60° C.

Step D Capsulation: 100 parts of the above emulsion accelerator liquid from Step B is stirred at 60° C. at 3,000 rpm using a TK Homomixer Mark II 20 (manufactured by Tokushu Kika Kogyo Co., Ltd.), 100 parts of the above encapsulation material from Step A is added and emulsified, the rotational speed is then gradually raised, and stirring is conducted at 7,000 rpm for 30 minutes, yielding an emulsion in which the average particle size of the oil droplets of the encapsulation material is approximately 3 μm (as measured by a laser diffraction particle size analyzer SALD-3100 (manufactured by Shimadzu Corporation). This analyzer is also used to measure all subsequent particle sizes.

To this emulsion is added 50 parts of the above melamine resin prepolymer aqueous solution from Step C. Stirring is continued for 2 hours, thus generating a melamine resin membrane around the periphery of the encapsulation material, and forming a microcapsule slurry with a solid fraction concentration of approximately 40%.

Example 2 Production of Melamine Resin Membrane/Fragrance Microcapsules (In Situ Polymerization Method)

An encapsulation material (A) is prepared by mixing 75% of the mint fragrance and 25% of behenyl alcohol (melting point: 70° C.) at 75° C., thereby dissolving the behenyl alcohol in the fragrance and forming a mixture. The melting point range for the thus obtained mixture is from 10 to 50° C. The mixture is held at 60° C. to prevent it FROM solidifying prior to emulsification.

With the exception of using this encapsulation material (A), a microcapsule slurry with a solid fraction concentration of approximately 40% is prepared in the same manner as the Example 1.

Example 3 Production of Melamine Resin Membrane/Fragrance Microcapsules (In Situ Polymerization Method)

An encapsulation material (A) is prepared by mixing 65% of the mint fragrance and 35% of paraffin wax (EMW-0003, manufactured by Nippon Seiro Co., Ltd., melting point: 50° C.) at 60° C., thereby dissolving the paraffin wax in the fragrance and forming a mixture. The melting point range for the thus obtained mixture is from 0 to 40° C. The mixture is held at 50° C. to prevent it solidifying prior to emulsification.

With the exception of using this encapsulation material (A), a microcapsule slurry with a solid fraction concentration of approximately 40% is prepared in the same manner as the Example 1.

Example 4 Production of Urea-Formalin Resin Membrane/Fragrance Microcapsules (In Situ Polymerization Method)

10% of a urea resin monomer (reagent grade, manufactured by Nissan Chemical Industries, Ltd.), 2% of a resorcin resin monomer (reagent grade, manufactured by Mitsui Chemicals, Inc.), and 3% of an ethylene maleic anhydride resin (Scripset-520, manufactured by Monsanto Company) are dissolved in 85% of water, and the solution is adjusted to pH 3 using acetic acid.

50 parts of the thus obtained aqueous solution is heated to 60° C., 40 parts of the same encapsulation material as the example 1 is added and emulsified, and stirring is conducted for approximately 30 minutes, until oil droplets with an average particle size of 3 μm had been formed. To this emulsion is added 10 parts of formaldehyde, and stirring is then continued for 2 hours, thus generating a urea-formalin resin around the periphery of the encapsulation material, and forming a microcapsule slurry with a solid fraction concentration of approximately 40%.

Example 5 Scented Quick-Set Lithographic Ink

Offset Ink Base is combined with other ink components to produce a Quick-Set lithographic ink as follows:

Ingredient Weight % Offset Ink Base 50.0 Quick Set Gel Vehicle 12.5 Quick Set Free Flow Vehicle 7.5 12% Cobalt Drier 1.0 6% Manganese Drier 1.0 Ink Oil (IBP 510 deg. F.) 3.0 Scented Microcapsule Slurry* 25.0 TOTAL 100.0 *This material is produced in any one of Examples 1, 2, 3 or 4.

Example 6 Rub Resistant Ink

To the ink described in Example 5 is added a finely divided microcrystalline wax, polyethylene wax, Fisher-Tropsch wax, either alone or in combination with a finely divided polytetrafluorethylene polymer, is added to the ink to improve the dry rub resistance of the dried ink film. Additions of dry wax may be made from 0.5% to 3.0%. Additions of compounded waxes may be from 1.5% to 10%, depending on the wax compound used should not exceed 15.

Example 7 Hard Drying Ink

Offset Ink Base is combined with other ink components to produce a hard drying, high solids ink as follows:

Ingredient Weight % Offset Ink Base 50.0 High Solids Gel Vehicle 10.0 High-solids Free Flow Vehicle 10.0 12% Cobalt Drier 1.0 6% Manganese Drier 1.0 Ink Oil (IBP 510 deg. F.) Litho Varnish 3.0 Scented Microcapsule Slurry* 25.0 TOTAL 100.0

Metal Decoration

An ink or coating may be applied to aluminum to make a beverage can with both scent and thermochromic attributes. The coating may be applied using conventional metal decorating equipment. The coating can be applied to any part of a can including the base or bottom, the side walls, neck, top surface, and the pull tab. The vehicle can be waterbased, solvent based, ultraviolet or radiation curable, heatset, two part epoxy, or one part epoxy but is not limited to these examples. The coating may also be prepared by using one epoxy coating for metal decorating, such as those sold by companies like Valspar or Watson Coatings. Thermochromic pigment loading is preferably between 1% and 30%, and most preferably is about 15%.

The aluminum stock may be roller coated, dipped, spray coated, or printed. The coating is prepared by adding a thermochromic to the vehicle or to a component in the finished vehicle. The thermochromic pigment may be dry or may contain between 0-50% moisture. The coating may be ready to use or be mixed with solvent, known by those skilled in the art, to a specific viscosity prior to use. It is preferable that the thermochromic microencapsulated pigment have adequate solvent resistance. The thermochromic microencapsulated pigment may be introduced to the vehicle using any mixer known to the art. The coating may be made in a batch process or in a continuous process.

FIG. 2 compares identical beverage cans 200, 300, which differ in that can 200 is a room temperature and can 300 is chilled. Lids 202, 302 are coated with epoxy-based thermochromic coatings 204, 304. As shown in FIG. 2, the relative darkness of lid 302 indicates that the beverage is sufficiently chilled to a recommended temperature for improved palatability. The lid 302 may optionally contain scented microcapsules to complement the beverage by imparting, for example, a cherry scent or a citrus scent. As is known in the art, the lids 202, 302 contain tabs that may be pulled to open access to space within the interior walls of cans 200, 300, such that liquid or other matter may be poured into or out of the cans 200, 300. As opposed to placing thermochromic ink on the entire lid, it is possible to coat just the tab 206, 306 s, or both the lids 202, 302 and the tabs 206, 306.

The instrumentalities of this disclosure are taught by way of non-limiting example according to the specific formulations described below.

Example 8 Two Part Epoxy

15% Thermochromic Pigment (any color)

15% Scented microcapsule slurry*

50% Epoxy Part A (Epoxy.com)

20% Hardener Part B (Epoxy.com)

100% Coating C

*This material may be as prepared in any of Examples 1, 2, 3 or 4. If scent is not desired, this material may be eliminated and the thermochromic pigment increased to 30%.

Cut ‘Coating C’ with Xylene (1:1). Once cut with solvent, the coating may be applied by roller coating or sprayer, and has an open time of several hours.

Example 9 Heatset Epoxy

-   -   70% Clear Coating (an epoxy coating available from Watson         Standard of Pittsburgh, Pa.)     -   20% Thermochromic pigment (any color)     -   10% Scented microcapsule slurry*     -   100% Thermochromic Coating         *This material may be as prepared in any of Examples 1, 2, 3         or 4. If scent is not desired, this material may be eliminated         and the thermochromic pigment increased to 30%.

This coating may be cut with xylene (1:1) to a desired viscosity, applied using a roller coater, and baked for 5-18 seconds at 400° F.

FIG. 3 shows a beverage can 300 that contains an image 308 of a glass that is partially-full of beer. The image 308 is for example printed with a thermochromic ink, as described above, to provide a color change interface zone 310 corresponding to the approximate level of beer inside can 300. The image 308 is optionally but preferably provided with lime-scented microcapsules, such that the scent complements the organoleptic qualities of the beverage.

The image 308 is provided with a number of features that sense and inform a beverage drinker of the thermal quality of the beverage. The coating in region 312 has, for example, a yellow color phase (or any other color) when chilled to less than a full color point. This full color point may be associated by design with an intended temperature for the beverage. This may be, for example, a temperature according to a manufacturer's recommendation or a temperature of an average refrigerator. This may be any temperature ranging from 32° F. to 55° F. (0° C. to 13° C.) or any other temperature that is perceptibly cooler than normal room temperature in the intended environment of use. The coating of region 310 resides above a liquid level 311 and is warmed by ambient room temperature to an activation temperature that causes the color of image 308 to fade on a gradient from the interface level 311 towards region 314. Region 344 has transitioned upon warming to a clearing point temperature. The entire image 308 may be printed over a contrasting color background, such as a white background or a contrasting background of any other color, indicating that no beer is present.

It will be appreciated from the context of FIGS. 1A and 1B as applied to FIG. 3 that the hysteresis parameters of thermochromic pigments may be adjusted by expert formulation upon commercial order to decrease the length or span of region 310 from the interface 311 towards region 314. This may be done, for example, by reducing the separate with across the hysteresis window, as well as by making a sharper (more vertical) warming curve, such that the span reflects a total temperature change of less than two or three degrees centigrade.

A “BEER ME!” message 316 is printed from two different inks each having approximately the same color transition temperature, which here is referred to as the second color transition temperature. The message 316 is normally hidden from view, matching the color of a background 318. Upon sufficient warming to a predetermined value, such as 10° C. above the manufacturer's recommended serving temperature, the message 316 becomes visible to indicate that the beverage has warmed to a temperature where the organoleptic qualities of the beverage are less than optimal or may even begin to degrade. This predetermined value preferably differs from the clearing point of the image 308 by having a higher value. Thus, the sensed level indicator of interface 311 may more accurately depict a true liquid level with less regard for the organoleptic qualities of the beverage itself, while the message 316 is indicates poor thermal quality of the beverage.

The concept of a thermochromic level indicator may be expanded to encompass any container or package (collectively a housing) that holds a liquid or other matter that may be sensed by a thermal difference, such as ice. The concept extends also to a label that is placed on such containers or packages. By way of example, the level indicator may be placed on a bottle, jug, keg, bag, box, glass, aluminum two piece can, three piece can, pressure sensitive label, destructible label, or any other item that may bear a label indicator.

Package contents for such items may include, for example: liquid beverages including water, soda, or alcohol; or functional fluids such as hydraulic fluids, lubricants, paints, or fire suppressants.

The level indicator may be applied using ink that is adapted to particular processes, such as offset ink, metal decorating ink, flood coating, screen print, sheetfed ink, paint, gravure, inkjet, or spray paint. The ink may be applied to a label that is adhered to a container or package, or the ink may be applied directly onto the container or package. The ink for these processes may be formulated as heatset ink, solvent based ink, uv curable ink, epoxy ink, waterbased ink, or any other form of thermochromic ink. The thermochromic microcapsules may be formulated as urea-formaldehyde, melamine formaldehyde, protein, gelatin, or any other type of microcapsule. Specially formulated thermochromic inks having selected color transition temperatures across a wide range of color transition temperatures may be purchased on commercial order from Chromatic Technologies, Inc. of Colorado Springs, Colo.

Although a glass is described above as used for image 308, the indicator may assume any form of artwork. The level indicator may be as simple as a vertical line. The level indicator may also assume a representation of a particular object, such as a thermometer, the image of a glass as described above, a rainbow, or the entire outer coating of the can 300. Moreover, the level indicator may be printed directly onto the housing or a label that adheres to the housing.

The level indicator may be used by filling the can or other housing with the matter to the first level, chilling the can to a temperature exceeding a color transition temperature of the thermochromic ink, and removing matter from the can to arrive at the second level in an environment such that the environmental temperature warms a portion of the thermochromic ink above the second level to a level above the color transition temperature. The color change may then be observed to assess an approximate level of the matter within the can.

It will be appreciated that the foregoing embodiments may be altered in various ways. For example, the pigment may be entirely eliminated to make an overprint varnish. The scented microcapsules or thermochromic microcapsules may be eliminated or used in any combination with glitter to give the dried inks a sparkly appearance. The thermochromic inks may be provided with a color transition temperature such that they change color when scratched. 

1. A housing comprising a wall presenting an interior space capable of retaining matter at a first level within the wall; means for permitting the matter to exit from within the wall or enter into the wall such that the matter assumes a second level; the wall supporting a level indicator, the level indicator being formed of thermochromic ink, the thermochromic ink having a color transition temperature capable of acting as a level indicator by sensing temperature of the matter retained within the wall in an intended environment of use.
 2. The housing of claim 1, wherein the matter is a beverage and the wall is at least part of a beverage container.
 3. The housing of claim 1, wherein the level indicator is printed as an indicia representing an image of an object.
 4. The housing of claim 3 where the image is a glass.
 5. The housing of claim 3 where the image is a thermometer.
 6. The housing of claim 3 where the image is a rainbow.
 7. The housing of claim 3 where the image is a vertically oriented line.
 8. The housing of claim 1 wherein the thermochromic ink included scented microcapsules.
 9. A method of sensing a liquid level using the housing of claim 1, comprising: filling the housing with the matter to the first level; chilling the housing to a temperature exceeding a color transition temperature of the thermochromic ink; removing matter from the housing to arrive at the second level in an environment such that the environmental temperature warms a portion of the thermochromic ink above the second level to a level above the color transition temperature; and observing the color change to assess an approximate level of the matter within the housing. 